Oil well production can involve pumping a well fluid that is part oil and part water, i.e., an oil/water mixture. As an oil well becomes depleted of oil, a greater percentage of water is present and subsequently produced to the surface. The “produced” water often accounts for at least 80 to 90 percent of a total produced well fluid volume, thereby creating significant operational issues. For example, the produced water may require treatment and/or re-injection into a subterranean reservoir in order to dispose of the water and to help maintain reservoir pressure. Also, treating and disposing produced water can become quite costly.
One way to address those issues is through employment of a downhole device to separate oil and water and to re-inject the separated water, thereby minimizing production of unwanted water to surface. Reducing water produced to surface can allow reduction of required pump power, reduction of hydraulic losses, and simplification of surface equipment. Further, many of the costs associated with water treatment are reduced or eliminated.
However, successfully separating oil/water downhole and re-injecting the water is a relatively involved and sensitive process with many variables and factors that affect the efficiency and feasibility of such an operation. For example, the oil/water ratio can vary from well to well and can change significantly over the life of the well. Further, over time the required injection pressure for the separated water can tend to increase.